Precision calibrated phase shifter



June 5, 1956 J. R. RAGAZZINI ET AL PRECISION CALIBRATED PHASE SHIFTER Original Filed June 12, 1950 7 Sheets-Sheet 1 June 5, 1956 J. R. RAGAzzlNl ET AL 2,749,502

PRECISION CALIBRATED PHASE SHIF'TER Original Filed June 12, 1950 '7 Sheets-Sheet 2 H44 f7) n H I6 o- /ZZ z3 Ea Z9 Eb Afb zo /z @a 2f) u 2@ za D Nv o m zz 29 i l /Z L afd Mfr ren/*w Afb i@ Ec l E( E INVENTORS Job/rRRagdZz//y/and l off/,4. 2nde/7 gym, Ml Maf@ A 7 TURA/E YS June 5, 1956 J. R. RAGAZZINI ET AL Original Filed June l2, 1950 7 Sheets-Sheet 3 70 F/'q l 5/ 5d I 43 i f2 i f Z i l 50 a g l b n I'* Li g c C l g d 60 f J' M f 2.5 .L M-J A-uf 56 e? l g I a6 l i 6]/ 56 f L l 1 Q El 69 I. 6d; T40 i 67/ l JL- l v WFM/wf- ,v z; :l: :I

INVENTORS Jo/m/ Raqazz//w' ana Lof/1 A. Zaden A] TOR/vf ns June 5, 1956 J. R. RAGAzzxNl ETAL 2,749,502

PRECISION CALIBRATED PHASE SHIFTER original Filed June 12, 195o '7 Sheets-Sheet 4 ATTORNEYS 7 Sheets-Sheet 5 J. R. RAGAZZINI ET AL PRECISION CALIBRATED PHASE SHIFTER June 5, 1956 Original Filed June l2. 1950 INVENTORS Joh/7A. Ragazzi/vlam off/A. Zane/7 y m4a4q M (51u04 *5U/M7 AT TURNEYJ June 5, 1956 J. R. RAGAzzlNl ET A1. 2,749,502

PRECISION CALIBRATED PHASE SHIFTER Original Filed June l2, 1950 7 Sheets-Sheet 6 www RN\ SN d En TS NSX f e MQ IA 1|/ RLV /J l di n RQ x @E UA H/.uM/

s@ T5 SN |ITNNM||||| l l I INR Q NSN j @m7 A T TOR/v5 rs June 5, 1956 J. R. RAGAZZINI ET AL 2,749,502

PRECISION CALIBRATED PHASE SHIFTER A T TOR/VE )1S 2,749,502 PRECISIGN CAMBRATEB PHASE SHIFTER John R. Ragazzini and Lofti Zadels, New York, N. Y.

Original application .lune 12, 195), Serial No. 167,550. Divided and this appiieatien February 9, 1954, Serial No. 412,194

Claims. (Cl. S23- 111) This application is a division of application Serial Number 167,550, filed June 12, 1950.

The present invention relates to a phase shifter and particularly to a precision calibrated phase shifter for use in apparatus for measuring the phase angle between two voltages.

An object of the invention is to provide an improved phase meter having a direct reading calibrated phase shifter.

Another object is to provide a phase meter having a phase angle scale which is independent of frequency.

A further object is to measure phase differences with .high precision over a wide range of frequencies.

Another object is to provide a phase meter of relatively simple construction adapted for high precision phase angle measurements, and adapted for very simple construction at low cost when measurements of relatively low precision are adequate.

Another object is to measure phase angle differences over a broad band of frequencies without requiring the use of a heterodyne operation and the complications and difliculties inherent with such a heterodyne operation.

Another object is to provide a phase meter in which i the actual measurement of phase is accomplished by a single control element, all other control operations being auxiliary to the adjustment of Voltage and independent of the actual setting of the phase angle measurement control element.

These and other objects and features of the invention will be understood from the following detailed description in connection with the accompanying drawings, in which:

Fig. l is a schematic circuit diagram showing the general arrangement for making phase angle measurements;

Figure 2 is a circuit diagram of a phase shifting amplifier of the integrator type, and Fig. 3 a similar diagram of a phase shifting amplifier of the differentiator type.

Figures 4 and 6 are schematic diagrams of calibrated phase shifters adapted for use in the phase meter of Fig. l.

Figures 5 and 7 are vector diagrams illustrating the operation of the circuits of Figures 4 and 6, respectively;

Figs. 8A, 8B and 8C are circuit diagrams of one form of phase meter; and

Figs. .9A and 9B are circuit diagrams of a modified form of phase meter.

In Fig. l we have indicated a simple fo-rm of block diagram fundamental to our invention. In this diagram E1 and E2 are the voltages the phase difference of which is to be measured. The voltage E2 is transmitted directly to the vertical plates of a standard oscillograph 53. E1 is transmitted through two components, the first being a calibrated phase shifter 20, and the second being a non-calibrated phase shifter 21, the output of which is fed to the horizontal plates of the oscillograph.

The method of measurement consists of first placing switch in its upward position, so that the voltage E1 is supplied to both channels. The calibrated phase Ashifter 20 is originally set to zero because the voltages are from the same source E1 and therefore have a zero phase difference. The non-calibrated phase shifter 21 is now States Patent lil adjusted until the trace on the oscillograph 53 is a collapsed ellipse, indicating that the phase shift in both channels is identical.

The switch 30 is then thrown to the lower position, so that now voltage E1 is in the first channel and E2 is in the second channel. The collapsed ellipse is restored by adjustment of the calibrated phase shifter Ztl until it is collapsed once again, and the amount of phase shift that had to be inserted in the calibrated phase shifter is the phase difference between the two voltages E1 and E2.

Fig. 4 shows one form of calibrated phase shifter which employs as a component thereof a phase shifting feed back amplifier of the integrator type, shown in Fig. 2, in which the amplifier has the variable resistor R in the upper input conductor and the capacitor C connecting the upper input conductor to the upper output conductor. The input voltage Ea produces the output voltage Eb which is displaced in a leading direction from the input voltage Ea. The precision of this 90 displacement is determined by the gain of the amplifier A and the quality of the capacitor C.

Instead of employing a phase shifting feed back ampliier of the integrator type, as shown in Fig. 2, as a component of the calibrated phase shifter, a phase shifting feed back amplifier of the differentiator type, as shown in Fig. 3, may be substituted therefor. It will be seen that the integrator of Fig. 2 is similar to the differentiator of Fig. 3, except that the resistor R and the capacitor C are interchanged in position in the two figures. In the integrator type of amplifier, the output voltage leads the input voltage by 90 whereas in the differentiator type, the output voltage lags 90 behind the input voltage.

The amplifier' 29, Fig. 4, corresponds with amplifier A, Fig. 2; the variable resistor 26, Fig. 4, corresponds with the resistor R, Fig. 2; and the capacitor 27, Fig. 4, corresponds with the capacitor C, Fig. 2. At the output of the amplifier 29, Fig. 4, is provided an adjustable potentiometer 22, the output voltage Eb being impressed across this potentiometer. A summing network, consisting of resistors 23, 24 and 25, is used to add the voltage Ea and a fraction AE1), of the voltage Eb. The adder resistors 23 and Z4 are made closely equal to each other, preferably within 1% or better when high accuracy is desired. The variable resistor 26 corresponds t0 resistor R, Fig. 2, and capacitor 27, Fig. 4, corresponds to the capacitor C of Fig. 2.

In the initial adjustment of the phase shifter, Fig. 4, the input voltage Ea is impressed across the input coupling resistor 28. The magnitude of the output voltage Eb is adjusted to be precisely equal to that of Ea, by adjusting the resistor 26. This is achieved when the product RCw equals l, where w is 2n times the frequency. y For example, in the vector diagram of Fig. 5, Eb is shown equal in magnitude to Ea and as leading Ea by 90. The fraction AEb of Eb that is added to Ea will determine the phase 6 of the resultant vector Ec. 6 is precisely known from the relation In the process of calibration, account is taken of the loading effect of resistor 23, in Figs. 4 and 6. The maximum phase displacement that can be produced by this process is limited to 45. This is an advantage,

tan 0:

since this makes it possible to provide a nearly linear scale.

Fig. 6 shows the manner in which the circuit of the calibrated phase shifter is altered so that the phase shift range can be extended from 45 to 90. Again, the integrator type of circuit is used as an example, and the calibrated potentiometer 22 is now connected across the input voltage Ea, instead of across the output voltage Eb as in Fig. 4, and a fraction AEs of Ea is now added through the same summing network 23, 24, 25 to the full value of Eb.

It will be noted that the coupling resistor 28 which is equal in resistance to potentiometer 22, is interchanged in position with potentiometer 22 to avoid undesirable changes in the circuit when these resistances are interchanged. While resistor 23 is not essential to the basic operation of the circuit of Fig. 6, it is desirable from the standpoint o-f good circuit design.

The vector diagram, Fig. 7, shows the angle as being in the sector extending from 45 to 90. It will be observed from the diagram that the angle 0 is now equal to the angle whose tangent is Eb AEG Figs. 8A, 8B, and 8C show a schematic diagram of a complete phase meter according to Fig. l and including a calibrated phase shifter of the integrator type according to Figs. 2, 4 and 6.

In Fig. 8A, the voltage input terminals 40 and 41 have the voltage Ei applied thereto, and the voltage input terminals 42 and 43 have the voltage E2 applied thereto. The voltages E1 and E2 are shown as being derived from a circuit 50 under test, having a supply Voltage E1 connected to the input terminals 44 and 45 thereof, and a voltage Ez at the output thereof. The purpose of this particular test circuit arrangement is to measure the phase difference between the input voltage E1 and the output voltage E2.

The switch 51 corresponds with the switch 30 in Fig. 1, except that the lower pole of switch 30 is replaced by a permanent connection between the lower terminals for E1 and E2.

The calibrated phase shifter of Fig. l is included in the circuit of Fig. 8B. The non-calibrated phase shifter 21 of Fig. 1 is included in the circuit of Fig. 8C. The oscillograph 53 of Fig. l is shown also in Fig. 8C.

The lower channel conductors 54 and 55 in Fig l, which connect directly to the vertical deflecting input terminals of the oscillograph 53, correspond to the conductors 54 and 55 in Figs. 8A, 8B and 8C. The upper channel conductors 56, 56a and 56h of Fig. l correspond to conductors 56 and 56 in Fig. 8A, conductors 56 and 56a in Fig. 8B, and conductors 56a and 56b in Fig. 8C, While conductors 57, 57a and 57b in Fig. l, correspond to conductor 55 in Figs. 8A, 8B and 8C.

In Fig. 8A the switches 60 and 61 have the four positions (a), (b), (c) and (d), respectively, and are ganged together to operate in unison as indicated by the dotted line 62. When the switch 60 is in position (a) or (b), the input potential applied to terminals 40-41 E1 connects with channel 55, 56. When in positions (c) and (d), switch 60 connects the input potential applied to terminals 40-41 E1 with the other channel 54, 55. Switch 61, when in positions (a) or (b), connects the other input potential E2 with channel 54, 55, and in positions (c) or (d) connects E2 with channel 55, 56.

When input potential Ei connects with channel 55, 56 with switch 60 in position (a) or (b), the voltage E1 is transmitted through the capacitor 63 to the potentiometer 64, whose sliding contact 65 connects with the grid of triode 66, having the grid leak resistor 69. The cathode follower resistor 67 is coupled by the capacitor 68 with conductor 56 which extends to the calibrated phase shifter shown in Fig. 8B.

The triode 66 serves as an isolating stage to provide the desired impedance transformation between the source E1 or E2 and the input conductors 55, 56 of the calibrated phase shifter circuit of Fig. 8B.

A suitable source of current, such as the alternating current rectifier 70, Fig. 8A, is provided for energizing the direct current circuits of the electron discharge devices of Figs. 8A, 8B and 8C, the cathodes being heated in well known manner by the usual heater element, not shown.

In the calibrated phase shifter of Fig. 8B, the electron discharge devices 71, 72 and 73 serve as voltage amplifiers, corresponding in function with the amplifier 29 in Figs. 4 and 6. The fixed resistor 74 is connected to conductor 56 and in series with the fixed resistor 75 shunted by the variable resistor 76. Resistors 74, 75, 76 provide a variable resistance network connecting conductor 56' to tbe grid of triode 71 and to conductor S4, and corresponding with the variable series input resistor 26 in Figs, 4 and 6.

The capacitors 80, 81, 82, 83, Fig. 8B, of different capacitance values are selectively connectable one at a time in series with the conductor 84, by the rotary switch 85, which has the four contact positions (a), (b), (c) and (d), respectively, the selected capacitor corresponding with feedback capacitor 27, Figs. 4 and 6.

The triode 71 is provided with a cathode follower resistor 86, which is included in the cathode to control grid circuit of pentode 72, and thus serves as a coupling between the output of triode 71 and the input of pentode 72. Resistor 86 is shunted by the capacitor 87. The grid leak resistor 110, for the grid of triode 71, is connected between conductors 56 and 55. The anode of triode 71 is supplied with a positive potential by rectifier 70 (Fig. 8A).

The positive screen grid potential in pentode 72 is reduced to the proper value by resistor 88, connected to rectifier 70, a bypass capacitor 89 connecting the screen grid with conductor 55. The suppressor grid of pentode 72 is connected directly with the cathode. The anode of pentode 72 is connected through output resistor 90 with a positive terminal of the rectifier 70 (Fig. 8A). The output of pentode 72 connects from the anode thereof to the left terminal of capacitor 91 which is shunted by a circuit comprising a resistor 92 in series with a capacitor 93, the right hand terminal of capacitor 91 being connected through resistor 94 with the control grid of pentode 73.

The cathode of pentode 73 has a voltage dropping resistor 95, shunted by the capacitor 96. The screen grid is connected through resistor 97 with a positive terminal of rectifier 70 (Fig. 8A), a bypass condenser 9S being connected between the screen grid and grounded conductor 55. The suppressor grid is connected directly with the cathode, while the anode is connected through the output coupling resistor 99 with a positive terminal of the rectifier 70, the anode being also connected to switch arm 85. Resistor 94 connects from the control grid of pentode 73 through the lead resistor 100 to the conductor 55.

Switches 101 and 102 have four positions (a), (b),

'(c) and (d), and are coupled together to operate in unison, as indicated by the dotted line 103, and are also coupled with switches 60 and 61, Fig. 8A, as indicated by the dotted line 120.

When switch 101 is in the position (a) or (d) it connects the anode or output circuit of pentode 73 through contact (a) or (d) of switch 101 with potentiometer 104, and from the slider through resistor 106 to the output conductor 56a, while switch 102 in position (a) or (d) connects the input conductor 56 through contact (a) or (d) of switch 102 through resistor 107 with the output conductor 56a of the calibrated phase shifter. The connection from the output conductor 56a to the input conductor 5,6', provides a feed back from the output to asf-sanos the input of the phase shifter, as indicated in Fig. 4, fby `the conductor including resistor 24. Potentiometer 104, Fig. 8B, corresponds with potentiometer 22, Fig. 4. Resistor 108, Fig. 8B, provides an output coupling across the output conductors 56a and 55 `of `the calibrated phase shifter. The resistors 106, 107 vand 108 are adder resistors corresponding respectively with the .adder resistors 23 24 and 25, Fig. 4. Resistor 109i, Fig. 8B, corresponds with the dummy load resistor 28 in Fig. 4.

When switches 101 and 102 are in positions (b) or (c), the potentiometer 104 and resistor 166 are transferred from the output of the amplifier, as shown schematically by potentiometer 22. and resistor 23 in Fig. 4, to the input of the phase shifter, as shown schematically in Fig. 6, and the resistors 107 and 109 are transferred from the input of the phase shifter, as shown schematically by resistors 24 and 28, in Fig. 4, to the output of the amplifier as shown schematically in Fig. 6.

The interstage coupling network 9.1, 92, 53, is adjusted to stabilize the operation of the ampliiier by suppressing 'undesired oscillations.

in the non-calibrated phase shifter of Fig. 8C, the conductor 56a connects through the capacitor 150 with the grid of triode 151 which .serves as an isolating stage to provide the desired impedance transformation between the calibrated phase shifter of Fig. 8B and the uncalibrated phase shifter of Fig. 8C. A resistor 152 connects `the grid directly to the cathode of triode 151. The anode of triode 151 connects with a positive .terminal of rectifier 70, Fig. 8A.

Coupling resistor 153 connects the grid of triode 151 yto conductor 55. The cathode of vtriode 151 has a `cathode follower resistor 154 which connects through a capacitor 155 to the coupling resistor 164 and also to the conductor 169.

Conductor 169 connects with the group of capacitors 156, 157, 158, 159 anyone capacitor of which is selectable by the rotary switch 160, having respectively the four contact positions (a), (b), (c), (d).

The 180 phase shift switches 161 and 181 are coupled together as indicated by the dotted line 182, to operated in unison between contacts (a) and (b). The grid of `triode 162 connects through the lead resistor 163 to conductor 55, the grid also being connected Vto switch 161. The variable resistor 165 connects switch 160 to grounded conductor 55.

The cathode of triode 162 is provided with a cathode follower resistor 166 which is also included in the cathode .to control the grid circuit of triode 167 and serves as .a coupling between these. triodes. The anode circuit of triode 162 is energized from a positive terminal of rectifier 70, Fig. 8A, and the anode circuit of triode 167 is energized through resistor 168 from a positive terminal of rectifier 70. The output circuit of triode 167 connects from the anode thereof through `the capacitor 170 and the phase meter output resistor 173 to conductor 55, and also connects to the contact (b) of the rotary switch l171 which in turn connects with conductor 56b leading to the upper horizontal detiecting input connection of oscil- -lograph 53, the lower horizontal deiiecting input connection of oscillograph 53 being connected to grounded conductor 55. The grid of triode 167 connects through the leak resistor 172 with grounded conductor 55, the grid also being connected to the rotary switch 181.

Conductor 169 connects through a variable resistor 175 to the rotary switch 176, having the four contact positions (a), (b), (c) and (d) connected respectively to the capacitors 177, 178, 179 and 180, the other terminals of which are connected to conductor 55. Switch 176 `is coupled with switch 160, Fig. 8C, to operate in unison therewith, as indicated by the dotted line 190, and in unison with switch 85, Fig. 8B, as indicated by dotted `line 174.

The 'variable resistor 175, Fig. 8C, connects conductor 169 to switch 176, and is coupled with variable resistor 165, as indicatedby the dotted line 185, to permit -of operation of these resistors in unison with each other- It will be seen that resistor 165 in series with the capacitor selected by switch 160 from the -group of capacitors 156 to 159, forms one arm of a bridge between conductor 169 and conductor 55. The other arm of the bridge includes the resistor 175 in series with switch 176 and the capacitor selected thereby in the group of capacitors 177 to 180. When switch 161 is in position (a) it will be noted that the grid of triode 162 connects with switch arm 160, while the grid of triode 167 connects with yswitch arm 176. When switch 161 is in position (b) the grid connections are interchanged, so that the grid lof triode 162 connects with switch arm 176 and the grid of triode 167 connects with the switch arm 160.

Rotary switch 171 .is provided with a contact (a) counected to conductor 187 connecting directly with the upper input conductor 56' of the calibrated phase shifter of Figure 8B, so that when switch 171 is in position (a), the .input voltage of the calibrated phase shifter, which corresponds with voltage Es in Figs. 4 and 5, .is applied directly to the horizontal input of oscillograph 53.

When switch 171 is in position (c), the horizontal input of the oscillograph v53 is connected through contact (c) of .switch 171 and conductor 188 with the anode of pentode 73, Figure 8B, so that the output voltage of the calibrated phase shifter amplifier, which corresponds with voltage Eb in Figs. 4 and 5, is applied directly to the horizontal input of the oscillograph 53. By comparing the oscillograph indications when switch 171 is in positions (a) and (c), the output voltage Eb of pentode 73 may be compared with the input voltage Ea across conductors 56', 55 and these voltages may be made equal by adjustment of resistor 76, Figure 8B, and by selection of the proper capacitors by the coupled switches of Fig. 8B, and 160 and 176 of Fig. 8C.

The non-calibrated phase shifting bridge arrangement, including the resistors 165 and 175, and thecapacitors selected by switches and 176, combined with triodes 162 and 167, make .it possible to shift the phase of the output voltage across coupling resistor 173 with respect to the input voltage across conductors 169 and 55 through any desired angle within a range of 180, it being merely necessary to shift the adjustment of the unitary controlled resistors and 175. The voltage across resistor 173 is equal to the difference between the voltage from the grid of triode 162 to the conductor 55 and the voltage .from the grid of triode 167 to the conductor 55, so that by throwing the unitary controlled switches 161, 181 from position (a) to position (b), the connections of the grids of these triodes are interchanged and a phase shift of is introduced in the output voltage `across resistor 173 with respect to that produced when switches 161 and 181 are in position (a).

Unitary controlled switches 85, Fig. 8B and 160 and 176, Fig. 8C, are frequency band switches for selecting capacitors of suitable value for use in different frequency bands, so that in any one position of these switches the capacitor selected by switch 85 has such a value that the product of 211- times the frequency, times the resistance of network 74, 75 and 76, times the capacitance of the capacitor selected by switch 85, equals 1, or wRC==1,`.as previously described in connection with Fig. 4.

In one example of a phase meter according to the circuit of Figs. 8A, 8B and 8C, the capacitors selectedby the switch 85, covered the following frequency ranges:

Frequency range in C. P. S.

The capacitors selected by switches 160 and 176 provide for the same ranges of frequency as those provided by the capacitors selected by switch 85.

Switches 60 and 61, Fig. 8A, together with switches 101 and 102, Fig. 8B, which will all operate together under unitary control, make it possible to employ the potentiometer 104 of the calibrated phase shifter to measure phase angles extending over a 360 range. In order to extend the range of the calibrated phase shifter of Fig. 8B beyond the range from to -90, to cover the range from 0 to +90, it is merely necessary to interchange the connection of voltages E1 and E2. This method is free from the possibility of producing a false indication on the oscillograph 53, because if E2 leads E1 (that is, by 90 or less), the potentiometer 104 can be adjusted until the oscilloscope 53 displays a collapsed ellipse ,indication of the correct slope which is standardized to be the same slope for all measurements with the phase meter of Figs. 8A, 8B, and SC. If on the other hand, E2 lags E1 (that is, by 90 or less), the phase shifter is not capable of adjustment to produce a collapsed ellipse of the correct slope on the oscillograph 53, and it is only possible to produce such an indication of a collapsed ellipse of the correct slope by interchanging E1, E2. The switches 60, 61, Fig. 8A are provided for accompiishing this interchange of Ei and E2.

When the switches 60 and 61 are in position (a) the range covers from 0 to -45; in position (b), the range covers from 45 to -90; in position (c), the range is |45 to +90; and in the position (d), the range is zero degrees to +45. The ranges so far described of these switches, thus extend from -90 through 0 to +90.

In order to extend the range of the phase meter to cover phase angles from 90 to -180 and from +90 to +180", the unitary controlled switches 161 and 181, Fig. 8C, are switched from contacts (a) to (b), and 180 is then added to each reading of the angle on potentiometer 104, Fig. 8B.

When operating the phase meter of Figs. 8A, 8B and 8C, the following procedure may be observed:

The source of voltage E1 is first connected to the terminals 40 and 41 of Figure 8A. Switch 60 and the other switches ganged thereto, are placed in position (a). Switch 171 is placed in position (a). The input voltage across conductors 55, 56' of the calibrated phase shifter of Fig. 8B is then made equal to the output voltage of the amplifier 73 by equalizing the indication produced on the oscillograph 53. The voltage equalization is accomplished by alternately connecting the switch 171, Fig. 8C, to positions (a) and (c) while adjusting the resistor 76, Fig. 8B, and, if necessary, adjusting the positions of the switch 85 with its ganged switches. When the voltages are equalized. they correspond to the equalized voltages Ea and Eb in Fig. 4, as previously described.

Switch 171 is then placed on (b), switch 161 at position (a), and switch 51 atits upper position. The potentiometer 104 is then set on 0, that is, at its lower limit of adjustment.

The uncalibrated phase shifter of Fig. SC is then adjusted by adjustment of the resistor 165 with its ganged resistor 175 until the oscillograph 53 displays a collapsed ellipse which slopes either upward or downward, this fact being noted for future reference as hereinafter explained.

The source of the voltage Ez, if not already connected, may then be connected to the terminals 42, 43, Fig. 8A. Switch 51 is then placed in its lower position. Potentiometer 104 is then adjusted through its 45 range, or until the oscillograph 53 displays a collapsed ellipse which slopes in the same direction as noted in the reference above. If the ellipse fails to so collapse,switch 60 is moved to position (b) and the potentiometer 104 is again adjusted in search of a balance, and if no such balance is obtained, as indicated by the oscillograph 53, switch 60 is moved successively to positions (c) and (d), while repeating the adjustment of potentiometer 104. If no balance is obtained thus far, switch 161 is moved to position (b) and the above procedure of adjusting potentiometer 104 for each position of switch 60 is followed until a balance is indicated by the oscillograph 53. After observing a few measurements so that the operator becomes familiar with the operation of the phase meter, the procedure may be considerably simplified by turning switches 60 and 161 to their proper final positions without going through all of the above described intermediate steps.

The potentiometer 104 is calibrated to read directly in angular measure, the phase shift introduced by the calibrated phase shifter of Fig. 8B, the 0 to 45 calibration being read when switch 60 is in position (a) or (d) and a 45 to 90 calibration being read when switch 60 is in position (b) or (c). A minus sign is placed before the angle read on potentiometer 104 when the phase balance is obtained with switch 60 in position (a) or (b), and a positive sign is placed before the angle, if the balance is obtained when switch 60 is in position (c) or (d). If the balance is obtained with switch 161 in position (a) nothing is added to the reading of potentiometer 104, while if switch 161 is in position (b) when the balance is obtained, is added to the angle reading.

Further measurements of the phase angle between E1 and Ez may now be made by merely adjusting the potentiometer 104 as long as the angle being measured remains within the 45 range of the potentiometer, for any given position of switch 60. If the phase angle to be measured extends outside of the 45 range of potentiometer 104 for which the switch 60 is set, it is then merely necessary to operate the switch 60 to its proper position and to make any needed operation of the switch 161 within the wide frequency range corresponding to any one setting of the band switch 85.

It will be seen that after preliminary adjustment of the phase meter, the phase angle between the voltages E1 and E2 can be accurately measured by merely adjusting a single control element, namely potentiometer 104, and reading its scale. If, after the preliminary adjustment, the phase angle between E1 and E2 has changed but the frequency of E1 and Ez is the same, the only control that need be operated to make the measurement is the potentiometer 104. If the amplitude of either E1 and/or E2 change but the frequency and phase angles of Ei and Ez remain the same, no change in the adjustment of the control element 104 need be made. If the frequency changes after the preliminary adjustment, the meter must be completely readjusted. However, the dial calibration of the potentiometer 104 remains the same at all frequencies within the operating frequency range of the instrument.

Figs. 9A and 9B illustrate a circuit similar to that of Figs. 8A, 8B and 8C, except that the differentiator type of calibrated phase shifter is employed, as shown schematically in Fig. 3, in place of the integrator type, shown in Fig. 2. It will be noted that some of the parts in Figs. 9A and 9B which are similar to corresponding parts in Figs. 8A, 8B and 8C, are given the same reference numerals distinguished by primes. It will be also noted that in Figs. 9A and 9B, the input voltage E1 and the input voltage E2 are interchanged from the positions shown in Fig. 8A, so that when the ganged rotary switches 200 and 201, in Fig. 9A, are in the position (a), the voltage Ei is connected directly from input terminals 202 and 203 to the vertical deflecting input terminals of the oscillograph 53g, Fig. 9B, over a path which may be traced from the upper input terminal 202 for voltage E1, the lower contact of switch 204, to switch 204 and conductor 205 to switch 201, through contact (a) of switch 201 and conductor 206, to the upper vertical deflecting terminal of oscillograph 53, and returning from the lower vertical deflecting terminal of oscillograph 53, to grounded conductor 208, leading to conductor 207 and terminal 203, Fig. 9A. The described amas-a path for voltage E1 thus corresponds with the lower channel in Fig. l..

The voltage E2 in Fig. 9A. is connected at input terminals 210 and 211, through a calibrated phase shifter, Fig. 9A, and a non-calibrated phase shifter, Fig. 9B, to the horizontal deflecting input terminals of the oscillo- `graph V53, Fig. 9B, similarly to the connection in Fig. 1 of voltage E1 to the horizontal deflecting input terminals of the oscillograph '53. The path for voltage E2 in Figs. ,9A and `9B may be traced from the upper input terminal V210, to switch 200, over contact (a), conductor 212, isolating amplifier 213, conductor v214, voltage ampliers 215, 216 and 217 in cascade in the calibrated phase shifter, over output conductor 218 of the calibrated phase shifter, and then lto Fig. 9B, over isolating amplifier 151', to conductor 220, forming the input conductor of the non-calibrated phase shifter, including electron discharge devices 162' and 167 'to the output conductor 223, connected to the upper horizontal deflecting input terminal of oscillograph '53. The return path from the oscillograph may be traced from the lower horizontal terminal thereof, over conductor 208, to Fig. 9A, and directly to the lower input terminal 211 for the voltage E2.

In Fig. 9A, the isolating amplifier 213 corresponds in function with the isolating amplifier 66 in Fig. 8A, and Vincludes similar elements in its circuit connections, as indicated by the same reference numerals with primes. The voltage amplifiers 215, 216, 217 in the calibrated phase shifter in Fig. 9A, correspond with amplifiers 71, v72, 73 in Fig. 8B, and employ circuit connections which are similar to the amplifiers 71, 72, 73, Fig. 8B, except as will be noted hereinafter. The isolating amplifier 151', Fig. 9B, corresponds with the isolating amplifier 151 in Fig. 8C. The non-calibrated phase shifter triodes 162' and 167 in'Fig. 9B, correspond with triodes 162 and 167 in Fig. 8C. Conductors '-223 land 20S, Fig. 9B, connected to the horizontal deflecting input terminals of oscillo graph 53, Fig. 9B, correspond with conductors 56h and 55, respectively, in Fig. 8C.

Rotary switches 230 and 231, Fig. 9A, are coupled together to operate in unison, as indicated by the dotted line 232, and are also coupled with switches 200 and 201, to operate in unison therewith as indicated by the dotted line 233. Switches 230 and 231, Fig. 9A, correspond with switches 101 and 102, Fig. 8B. Conductor 214 is connected to capacitors 235, 236, 237 and 238, any one of which is selectable by the rotary switch arm 239, having the contacts (a), (b), (C.) and (d). Switch 239 connects through the coupling capacitor 240 with the grid of triode 215 having the grid leak resistor 219.

The cathode follower resistor 241, connected between the cathode of triode 215 and conductor 208, is included in 'the cathode to control grid circuit of pentode 216 to provide a coupling between triode 215 and pentode 216. The pentode 2'16 has an output coupling resistor 224 in its lanode circuit. The anode of pentode 216 connects through the capacitor 242 to the control grid of pentode 217. The resistor 243 in series with the capacitor 244 is connected in shunt `with the capacitor 242 to provide a stabilizing network, corresponding with the network 91, 92 "93 in Fig. 8B.

The pentode 217, Fig. 9A, corresponds generally with the pentode 73, Fig. 8B, but it will be noted that the resistor corresponding with resistor 94, Fig. 8B, is omitted from Fig. 9A, and that the capacitor 245, Fig. 9A, which is included between the control grid and the anode of pentode 217, has no corresponding element in Fig. 8B.

Switch 239 connects through resistor 250 in series with resistor `251 to the anode of pentode 217, Fig. 9A, the resistor 251 being shunted by the variable resistor 252. The resistor network 250, 251, 252, corresponds with the variable resistor R in Fig. 3. The capacitor selected by switch 239, corresponds with the capacitor C in Fig. 3. The anode and other direct current circuits of triodes It) 213 and 215, and yof pentodes 216 and 217 are energized .from a suitable D. C. source, such as the rectifier 255 connected to an alternating current source.

The rectifier 255 has the transformer 400 with the primary 401 connected to the alternating current source, the secondary 402 having the grounded mid-tap 403, .and 'the cathode heating secondaries 404 and 405. The `terminals of secondary 402 are connected respectively to the two anodes of the rectifier tube 406, the cathode of which is heated from secondary 404 and is connected through the inductance 407 and capacitor 408 to ground. Elements 407 and 408 comprise the lirst section of a ripple suppressing filter having in cascade therewith a second section comprising .inductance 409 in series with capacitor 410, and a third section comprising the resistor 411 in series with the capacitor 412 having the resistor 413 in shunt therewith. The screen grid of pentode 216 is connected through resistor 414 with terminal 415 of the rectifier filter, the capacitor 416 being connected between the screen grid and grounded conductor 20S, the screen grid of pentode 217 being connected through the resistor 417 with the terminal 415, the capacitor 416 being connected between the screen grid and conductor 208.

The pentode 217 has a leak resistor 256 connecting its control grid with conductor 208, and has a cathode dropping resistor 257 shunted by the capacitor 258. The output coupling resistor 253 is connected between the anode of pentode 217 and rectifier 255. The anode of pentode 217 is connected to switch 230 which, in position (a), connects through potentiometer 259 with conductor 208. The sliding contact 260 on potentiometer 259 connects through resistor 261 to conductor 218. The output cou- ,pling resistor 262 vof the calibrated phase shifter of Fig. 9A, `connects conductor 213 with conductor 208. Conductor 214, at the input ofthe calibrated phase shifter, connects with conductor .263 leading to'switch v231 which, in position (a), connects with conductor 264 which in turn connects through resistor 265 to conductor 218. Conductor 264 also connects through resistor 266 to conductor 208.

'The measuring `potentiometer 259 corresponds with measuring potentiometer 104, Fig. 4. The combination of resistor 261, resistor 265 and resistor 262, Fig. 9A, provide an adder network, corresponding with the adder network in Fig. 4, including respectively, resistors 23, 24, 25. Resistor 266 serves as a dummy load for cornpensating for the transfer of potentiometer 259 from the output to the input of the calibrated phase shifter by means of switches 230 and 231, and corresponds with resistor y10.9, Fig. 8B.

The noncalibrated phase shifter shown in Fig. 9B is similar to that of Fig. 8C, except that switches 161 and 161 of Fig. 8C are omitted and permanent connections are provided corresponding with the circuit when switches 161 and 181 are in position (a). It will be noted that the frequency band switches 160', 176', Fig. 9B are coupled together as `indicated by dotted line 190, and are also coupled as indicated by dotted line 174 with switch 239, Fig. 9A, so that switches 239 (Fig. 9A) and 160', 176 (Fig. 9B), correspond respectively with switches (Fig. 8B) and 160, 176 (Fig. 8C).

Instead of employing koscillograph 53 for indicating equality of the input and output voltages of the calibrated phase shifter in Fig. 9A, vin the manner indicated in Fig. k8B and 8C, wherein switch 171, in its positions (a) and (c), connects the oscillograph with the input and output, respectively, of the phase shifter, a switch 270, Fig. 9A, in its upper position (a), connects the conductor 214, at the input of the calibrated phase shifter, with one terminal of a suitable voltage indicating device, such as the vacuum tube voltmeter 271, the other terminal of the voltmeter 271 being connected to conductor 272, leading to conductor 208. Switch 270 in its lower position (b), connects the voltmeter 271 to the output of the amplifier of the calibrated phase shifter at the anode of pentode 217. The input and output voltages of the amplifier may be adjusted to equality by operating switch 270 alternately to positions (a) and (b) while adjusting the variable resistor 252 and frequency band switch 239, Fig. 9A, until the voltmeter 271 indicates the same voltage for both positions of switch 270.

When operating the phase meter of Figs. 9A and 9B the procedure is similar to that already described in connection with Figs. 8A, 8B and 8C. The source of voltage Ei, however, is temporarily connected with terminals 210 and 211. Switch 200 and the other switches ganged thereto are placed in position (a). The input voltage Ea in the calibrated phase shifter (see Fig. 3 for general schematic diagram) between conductors 214 and 208, Fig. 9A, is then adjusted to equality with the output voltage Eb of the amplifiers 215, 216, 217 of the calibrated phase shifter between the anode of pentode 217 and conductor 208. Equalization of Ea and Eb is obtained by alternately positioning switch 270 in position (a) and (b), while adjusting resistor 252 and switch 239, as referred to above.

Switch 204 is then placed in its upper position. Potentiometer 259 is set on that is, at its lower limit of adjustment.

The uncalibrated phase shifter of Fig. 9B is then adjusted by adjustment of the resistor 165' with its ganged resistor 175 until the oscillograph 53 displays a collapsed ellipse in the form of a line which slopes either upward or downward, this fact being noted for future reference, as further explained hereinafter.

The source of voltage El is now removed from terminals 210 and 211 and the source of voltage E2 is connected in place thereof, the source E1 being connected with the terminals 202 and 203, as indicated in Fig. 9A. Switch 204 is then placed in its lower position. Potentiometer 259 is adjusted through its 45 range, or until the oscillograph 53 displaces a collapsed ellipse. If the ellipse fails to collapse, switch 200 is then operated to its next position and the potentiometer adjustments repeated, and so on for each position of switch 200 until a phase balance is indicated by a collapsed ellipse on the oscillograph.

The setting of potentiometer 259 is then read from its 0 to 45 calibration, if switch 200 is in position (a) or (d), and is read from its 45 to 90 calibration, if switch 200 is in position (b) or (c). A positive sign is placed before the angle reading of potentiometer 259 when the switch 200 is in position (a) or (b), and a negative sign is placed before the angle reading if the balance is obtained when switch 200 is in position (c) or (d).

If the collapsed ellipse on oscillograph 53 slopes upward while originally the slope of the collapse ellipse referred to above was downward, or vice versa, 180 is added to the reading of potentiometer 259. By observing the direction of the slope of the collapsed ellipse on the oscillograph 53, it will be seen that it is unnecessary to introduce a reversal of phase in the non-calibrated phase shifter, as is accomplished by switch 161 in Fig. 8C. The non-calibrated phase shifter is thus more simplied in Fig. 9B than in Fig. 8C. It will be understood Vthat the switches 161 and 181, Fig. 8C, may be left in position (a), or the circuit permanently connected in this form, without providing these switches, the necessity of adding 180 to the reading of the phase angle being determined as in the case of Figs. 9A and 9B.

The following are the values of resistors, capacitors, and other elements and voltages illustrative of one eX- ample of a phase meter constructed in accordance with the circuit of Figs. 9A and 9B. 1t will be understood, however, that various other values of the circuit elements can-be used in other examples of this circuit.

Resistors VReference numerals: Value in Ohms 64'; 243; 251; 256 meg 1 153'; 163; 219 500K 252 (variable) 500K 414; 417 250K 173'; 261; 265 200K 69'; 152'; 168' 100K 165'; 175' (variable) 100K 67'; 266 50K 259 (potentiometer) 50K 413 30K 224; 253 25K 262; 411 20K 116'; 264; 250 10K 154 5K Capacitors Reference numerals: Capacitances 258 af 412 af 30 216; 217; 408; 410; 416; 418 at 16 68'; 155'; 156'; 170'; 177'; 244 af l 63'; 157'; 178'; 242 af .l 235; 240 af .05 158'; 179 af .01 236 af .005 159'; 180' at .001 237 aaf `500 238 ,u.,u.f 100 245 ,uaf 5 Inductors 407; 409 henries 15 .Tubes i Reference numerals: Type 406 5U4G 217 6AC7 213; 215 615 216 6SJ7 162'; 167' 6SL7 Voltages 401 (60 C. P. S.) 125 402 2 440 404 5 405 6.3

we desire to cover by Letters Patent is set forth in the appended claims.

We claim:

1. A phase shifter having first and second input'terminals and first and second output terminals, a first resistor in shunt to said input terminals, a second resistor in shunt to said output terminals, a conductor connectlng said second input terminal directly to said second output terminal, an amplifier having a first input connection to said first input terminal, a second input connection to said conductor, and an output connection to said conductor, a third resistor having one end connected to said conductor and the other end connected to the output of said amplifier remote from said conductor, a first adder connection from a point on said third resistor remote from said conductor to said iirst output terminal, a tirst phase control impedance element in said first input connection, a feedback connection including a second phase control impedance element connecting the end of said first phase control impedance element remote from said first input terminal to the output of said amplifier remote from said conductor, and a second adder connection from a point on said first resistor remote from said conductor to said first output terminal, each of said adder connections including a resistor, one of said phase control impedance elements being a variable resistor and the other a capacitor.

2. A phase shifter according to claim l, having means for interchanging the connection of said first resistor with said first input terminal and the connection of said third resistor with the output of said amplifier remote from said conductor.

3. A phase shifter according to claim 2, wherein said third resistor is a potentiometer having a slider constituting the point of connection of said first adder connection with said third resistor.

4. A phase shifter according to claim 1, wherein said third resistor is a potentiometer having a slider constituting the point of connection of said first adder connection with said third resistor.

5. A phase shifter according to claim 4, wherein said potentiometer has a calibrated scale indicating directly the angle of phase shift of said shifter at a plurality of settings of said potentiometer independently of frequency Within a predetermined frequency band.

6. An adjustable phase shifter of the class described, comprising: an input circuit to which a wave to be shifted in phase is applied; quadrature means connected to said input circuit for producing a fixed 90 phase shift in said input wave; means for deriving two equal voltages differing in phase by 90 from said quadrature means and from said input circuit; calibrated adjustable effectively purely resistive means to which one of said voltages is applied, said calibrated means including means for selecting a measured fraction of said one voltage; means for vectorially adding said selected fraction of said voltage to the full Value of other of Said two voltages; and an output circuit to which the sum of said added voltages is applied.

7. A phase shifter according to claim 6, in which said quadrature means comprises means for maintaining said fixed 90 phase shift constant throughout a wide range of frequencies.

8. A phase shifter according to claim 7, wherein said quadrature means comprises a Wide band amplifier having an input and an output; a first circuit element connected in series with said amplifier input, and a second circuit element having an impedance equal to that of the first circuit element connected from the junction point between said amplifier input and said first circuit element to a point in the circuit of said amplifier output.

9. An adjustable phase shifter for shifting the phase of a sinusoidal voltage having any frequency in a wide range of frequencies through an accurately ascertainable angle, comprising: means for converting said sinusoidal voltage into two substantially equal voltages differing in phase from each other by an accurately fixed angle of 90 throughout said wide range of frequencies; means for selecting an accurately ascertainable fraction of one of said voltages; and adding means for vectorially combining said ascertainable fraction of said one voltage with the full value of the other of said two equal voltages, whereby said combining means produces a resultant voltage which is shifted in phase by an accurately ascertainable angle of which the tangent is an algebraic ratio between said fraction and unity including the reciprocal of said fraction.

l0. An adjustable phase shifter for producing an accurately ascertainable phase shift comprising: means for vectorially combining two equal sinusoidal voltages both derived from a sinusoidal voltage of which the quadrature phase relationship including calibrated means for selecting an ascertainable fraction of one of said voltages for com bination with other of said equal voltages, the angle of phase shift being ascertainable as being an angle of which the tangent is a ratio between said ascertainable fraction of said one voltage and the full value of said other voltage.

ll. A phase shifter of the class described, comprising: a first circuit means defining an input for a voltage wave which is to be shifted in phase by said phase shifter; a second circuit means defining an output to which said voltage wave is delivered after having been shifted in phase by said phase shifter; quadrature means having an input and an output, said quadrature means producing a precisely fixed angle of phase shift in a voltage wave passing therethrough from the input thereof to its output throughout a wide range of frequencies for said wave, the input of said quadrature means being connected with the input of said phase shifter; a first terminating resistor connected across said phase shifter input; a second terminating resistor connected across the output of said quadrature means; means for equalizing the amplitudes of the voltage waves at both of said terminating resistors; adjustable means connected with one of said terminating resistors for deriving therefrom a desired fraction of the voltage wave impressed thereon, from zero to the full value of said voltage wave; and adder means connected to the other of said terminating resistors; to said adjustable means and to said phase shifter output, said adder means combining the full value of said voltage wave at said other terminating resistor with said fraction of said wave derived by said adjustable means and delivering a wave corre sponding to the vector sum of said full value and fraction to said phase shifter output.

l2. A phase shifter according to claim 1l, further comprising a reversing switch connected with at least one of said terminating resistors for reversing the polarity of the voltage wave derived therefrom.

13. A phase shifter according to claim 11 wherein said one of said terminating resistors and said adjustable means together consist of an adjustable potentiometer.

14. A phase shifter according to claim 1l, further comprising switching means connected with both of said terminating resistors for selectively interchanging the positions of said terminating resistors in the circuit of said phase shifter, said adjustable means remaining connected with said one of said terminating resistors.

15. A phase shifter according to claim 11, further comprising switching means connected with both of said terminating resistors and including a two-pole switch having four positions to which it may be selectively operated, said switching means comprising a portion connected to reverse selectively the polarities of the voltage waves derived from said resistors, and a portion connected to interchange selectively the positions of said resistors in the circuit of said phase shifter.

References Cited in the file of this patent UNITED STATES PATENTS 2,481,492 Bjarnason Sept. 13, 1949 

